Conventionally, a liquid crystal display apparatus includes a liquid crystal panel in which: a plurality of scanning signal lines (gate signal lines) and a plurality of video signal lines (source signal lines) intersect with each other, and there are provided in a matrix manner a plurality of display pixels each of which is connected to the gate signal line and the source signal line so as to correspond to each of regions sectioned by both the lines. Each display pixel has: a liquid crystal capacitance Clc provided between a pixel electrode and a counter electrode; and a thin film transistor (TFT) whose gate electrode is connected to the gate signal line, whose source electrode is connected to the source signal line, and whose drain electrode is connected to the pixel electrode. As necessary, an auxiliary capacitance Cs is provided.
Source drivers are provided on a periphery of the liquid crystal panel so as to respectively correspond to the plurality of source signal lines, and each of the source drivers supplies, to a corresponding source signal line, a video signal for each display pixel connected to the source signal line. In order to prevent burn-out of liquid crystal, a positive polarity and a negative polarity of the video signal are alternately supplied to the counter electrode. Such driving of the liquid crystal panel is referred to as “inversion driving”.
Further, gate drivers are provided on the periphery of the liquid crystal panel so that each of the gate drivers corresponds to a certain number of plural gate signal lines, and each of the gate drivers supplies, to a corresponding gate signal line, a scanning signal for selectively driving each display pixel connected to the gate signal line.
In each pixel, when the TFT is turned ON by the scanning signal, a video signal is supplied to the pixel electrode via the TFT, orientation of liquid crystal serving as a display medium sandwiched by both the electrodes changes in accordance with a potential difference between a counter electrode potential and a pixel electrode potential, and various kinds of images as well as texts, figures, and the like are displayed in a display screen by the whole pixels.
In the liquid crystal display apparatus, not only the liquid crystal capacitance Clc and the auxiliary capacitance Cs but also a parasitic capacitance Cgd between the gate and the drain of the TFT exists in each display pixel. Thus, the gate-drain parasitic capacitance Cgd causes a charge pull-in voltage (charge pull-in amount) ΔV represented by the following equation to occur in each pixel, and a voltage actually applied to the liquid crystal changes by the charge pull-in amount ΔV. Note that, in the following (Equation 1), VGH represents a gate high voltage of the scanning signal line, and VGL represents a gate low voltage of the scanning signal line.ΔV={Cgd/(Cgd+Clc+Cs)}×(VGH−VGL)  (Equation 1)
Further, charge pull-in amounts ΔV are different from each other in the display screen of the liquid crystal panel, so that flicker occurs in the display screen (flicker phenomenon). The following two cases (1) and (2) are typical factors of the flicker phenomenon in the liquid crystal display apparatus.
(1) In the liquid crystal panel, a gate signal line has a wiring resistance and a parasitic capacitance, so that a waveform of a gate signal is more likely to be round as further away from a signal input terminal of the gate signal line, and the charge pull-in amounts ΔV each caused by the gate-drain parasitic capacitance Cgd become different from one another in the respective pixels. This difference between the charge pull-in amounts ΔV causes deviation between a center value of voltages applied to a liquid crystal layer at the time of positive-polarity driving and a center value of voltages applied to the liquid crystal layer at the time of negative-polarity driving, in the display screen of the liquid crystal panel. This causes imbalance, thereby resulting in occurrence of the flicker phenomenon.
(2) In the step of forming a pixel pattern on a glass substrate (glass board), an area size of the glass substrate may be so large that it is difficult to form the pixel pattern on the entire surface of the glass substrate by a single forming process, so that the forming process of the pixel pattern is performed plural times with respect to plural blocks into which the surface of the glass substrate is divided. In this case, due to an alignment position or a property of a pattern forming device, a deviation occurs between the gate-drain parasitic capacitances Cgd in the display screen of the liquid crystal panel. Due to the deviation between the parasitic capacitances Cgd, the difference occurs between the charge pull-in amounts ΔV each represented by the foregoing equation, so that deviation occurs between a center value of voltages applied to a liquid crystal layer at the time of positive-polarity driving and a center value of voltages applied to the liquid crystal layer at the time of negative-polarity driving, in the display screen of the liquid crystal panel. This results in the flicker phenomenon.
The flicker phenomenon (1) is caused by the round waveform of the gate signal. Generally, the gate signal lines are disposed in a horizontal direction in the display screen, so that it is possible to alleviate the flicker phenomenon by correcting a center value of the positive polarity gray scale voltage and a center value of the negative polarity gray scale voltage, in accordance with inclination of the charge pull-in amounts ΔV in the horizontal direction.
Further, the flicker phenomenon (2) is caused by the property in the step of forming the pixel pattern. Thus, in case where the forming process of the pixel pattern is performed plural times, it is possible to alleviate the flicker phenomenon by correcting the deviation between the charge pull-in amounts ΔV in respective formation blocks.
Further, for example, Patent Literature 1 discloses a liquid crystal display apparatus configured so that an element which can obtain a desired resistance value in response to an external input, e.g., a potentiometer, is incorporated into a gray scale voltage generation circuit so as to adjust a gray scale property without changing a circuit constant after designing a driving circuit.